Thanks to the rapid development of the electronic industry, the currently available electronic products now have electronic elements with largely upgraded performance and increased computing speed. However, with the constantly increased number and computing speed of chips inside the electronic elements, heat produced by these chips during operation thereof also increases. The heat produced by the working chips must be timely removed from the electronic elements, lest it should adversely affect the performance of the electronic elements to result in lowered computing speed thereof. Further, the electronic elements are subject to burnout when the heat accumulates without being timely removed from the electronic elements. Therefore, it has already become an important issue to effectively dissipate heat from the electronic elements. Currently, the use of a cooling fan is one of the most common ways of heat dissipation.
In a very limited system space, a small-sized centrifugal fan is frequently used as a cooling fan. FIGS. 1A, 1B and 1C illustrate a conventional centrifugal fan 1, which includes a fan frame 11, a top cover 12, a hub 13, and a plurality of blades 14 circumferentially spaced on an outer surface of the hub 13. The fan frame 11 is provided on a bottom with a lower air inlet 111, and the top cover 12 is closed onto a top of the fan frame 11 and provided with an upper air inlet 121. The assembled fan frame 11 and top cover 12 together define an air outlet 112 that is located on a lateral open side of the fan frame 11. The hub 13 and the blades 14 spaced thereon are mounted on the bottom of the fan frame 11 to locate between the fan frame 11 and the top cover 12. When the hub 13 rotates, the blades 14 are caused to rotate synchronously. At this point, external air is caused to flow into the centrifugal fan 1 via the lower air inlet 111 and the upper air inlet 121 in a direction parallel to the hub 13. The air axially flowing into the fan frame 11 then flows in a radial direction relative to the hub 13 before it finally flows out of the fan frame 11 via the air outlet 112.
In designing the centrifugal fan 1, an upper and a lower air-in space must exist above and below the hub 13, respectively. In other words, the upper air-in space is provided between the top cover 12 and the hub 13 and the blades 14, and the lower air-in space is provided between the fan frame 11 and the hub 13 and the blades 14. These air-in spaces inevitably increase an overall thickness of the centrifugal fan 1, preventing the same from having a slim design. On the other hand, omission of the air-in spaces would have adverse influence on the operational performance of the centrifugal fan 1. Moreover, with the air inlets 111, 121 formed on the bottom of the fan frame 11 and the top cover 12, increased noise will be produced when the hub 13 and the blades 14 rotate.
In brief, the conventional centrifugal fan has the following disadvantages: (1) uneasy to realize a slim design thereof; (2) having adverse influence on the fan's operational performance; and (3) tending to produce increased noise during fan operation.
It is therefore tried by the inventor to develop a slim fan structure that overcomes the disadvantages of the conventional centrifugal fan.